1. Field of the Invention
The present invention relates to an abrasing apparatus using magnetic abrasive powder, and more particularly to an abrasing apparatus in which the magnetic abrasive powder filled in a barrel is arranged to be formed in chain-like bridge by a magnetic field generated in the barrel so that the surface of a work is abrased by a magnetic brush formed by the arrangement of the magnetic abrasive powder. Specifically, the present invention relates to the abrasing apparatus capable of directing the arrangement of the magnetic abrasive powder to an optimum direction for the abrasion.
2. Prior Art
An abrasing apparatus using magnetic abrasive powder is employed to abrase the surface of a metal work such as a bobbin case equipped in a sewing machine to a mirror-like surface.
FIG. 8 illustrates a structure of the abrasing apparatus using magnetic abrasive powder which has been proposed heretofore. The abrasing apparatus of FIG. 8 is disclosed in Japanese Patent Application No. 219,378/82 filed Dec. 16, 1982 in the Japanese Patent Office with the claim of convention priority based on Bulgarian Patent Application No. 55,025 filed Jan. 18, 1982. The application was laid open to public inspection on Aug. 6, 1983 under Provisional Publication No. 132,455/83. The abrasing apparatus is now described with reference to the figure.
The abrasing apparatus comprises a rotary barrel 1. The barrel 1 is rotatably supported on a stand 3 through a bearing 2. A follower pulley 4 is integrally mounted to a lower portion of the barrel 1 and rotary motion or power of a drive pulley 5 mounted to a shaft of a motor 7 is transmitted to the follower pulley 4 through a belt 6 so that the barrel 1 is rotated. Magnetic abrasive powder 9 is filled in a bottom portion of the barrel 1. The magnetic flux generated from an exciting coil 8 passes between an upper ring 10a and a lower ring 10b of the barrel 1 so that the magnetic abrasive powder 9 is arranged by the magnetic flux to form the magnetic brush. A disk 11 is provided with a spindle 13 which is rotated by a motor 14. A work 15 is attached to a lower end of the spindle 13. The work 15 is inserted within the magnetic brush formed in the barrel 1 and the surface of the work 15 is abrased by the magnetic brush through rotation of the barrel 1 and the spindle 13.
In the abrasing apparatus using the magnetic abrasive powder, the abrasion condition of the surface of the work is controlled by the strength of the arrangement of the magnetic abrasive powder in the barrel. The strength of the arrangement of the magnetic abrasive powder is largely affected depending on the magnetic density in the barrel and the direction of the magnetic flux. Since the magnetic flux in the prior art abrasing apparatus of FIG. 8 is merely formed in the barrel vertically, the arrangement force of the magnetic abrasive powder is weak as a whole and the magnetic brush is formed fragilely and weakly. Accordingly, the prior art abrasing apparatus can not abrase the surface of the work such as the bobbin case of the sewing machine like the surface of the mirror.
FIG. 9 shows partially another abrasing apparatus using magnetic abrasive powder which has been proposed heretofore. The abrasing apparatus of FIG. 9 is disclosed in Japanese Patent Application No. 143,120/83 filed Aug. 6, 1983 in the Japanese Patent Office. The application was laid open to public inspection on Feb. 21, 1985 under Provisional Publication No. 34,264/85. The prior art abrasing apparatus includes a magnetic abrasive powder 9 filled in the rotary barrel 21 in the same manner as the apparatus of FIG. 8. A plurality of segment magnetic poles 28 are disposed on an inner plate in the barrel 21 in spaced relationship with each other. A plurality of segment magnetic poles 29 spaced from each other are also disposed on the outside of the outer plate 20 and a plurality of segment magnetic poles 26 are further disposed to a bottom in spaced relationship with each other. A spindle 24 holding a work 25 is inserted into the barrel 21 from the upside thereof and the work 25 is embedded in the magnetic abrasive powder 9. The magnetic flux generated from an exciting coil 23 penetrates within the barrel 21 through a yoke 22 while the magnetic flux within the barrel 21 concentrates in the segment magnetic poles 26, 28 and 29. Accordingly, the magnetic abrasive powder concentrates locally and the magnetic brush is also locally formed depending on the arrangement of the segment magnetic poles 26, 28 and 29. The surface of the work 25 is abrased by rotation of the barrel 21 and the spindle 24. At this time, the surface of the work 25 is abrased by the magnetic brush formed locally.
In the abrasing apparatus of FIG. 9, however, the magnetic flux extending in the barrel 21 from the segment magnetic poles 28 is bent downward. Accordingly, the directivity of the magnetic flux is weakened and the magnetic flux tends to be scattered. Hence, it is insufficient to concentrate the magnetic abrasive powder and it is impossible to form strong magnetic brush by concentrating the magnetic abrasive powder enough to achieve an object of the present invention. Specifically, the force of the magnetic abrasive powder concentrating on the upper surface of the work can not be strong and the upper surface of the work can not be abrased like the surface of a mirror. A part of the magnetic flux is directed to the segment magnetic poles 29 provided outside. The magnetic flux directed to the outside magnetic poles 29 penetrates the poles 29 and is returned to the exciting coil 23 through the lower side of the barrel 21. Accordingly, since the magnetic circuit is long and the magnetic flux is scattered to be directed to the bottom and the outside of the barrel 21, the magnetic flux can not be utilized effectively. The arrangement force of the magnetic abrasive powder is reduced throughout the barrel.